Pool running: two words that strike fear into the heart of injured runners everywhere. It’s the ultimate cross-training and rehab exercise, because it has zero impact and is thought to most closely emulate the motion of running. There have been plenty of studies on the cardiorespiratory effects of pool running — anyone who has tried it will tell you that you have to work harder to get your heart rate to its usual levels (and to avoid stabbing yourself in the eye out of sheer boredom). But there has been surprisingly little study of how your muscles actually get used in pool running.

Researchers from the University of Nevada, Las Vegas have finally performed such a study. They took a group of seven runners, wired them up with electrodes on various parts of their legs, and had them run at various intensities first on a treadmill, then in the pool (wearing drysuits to keep from zapping themselves). The results: tibialis anterior (shin) and gastrocnemius (calf) activations were way lower in the pool than on land. Rectus femoris (quad) and biceps femoris (hamstring) activation was a little more ambiguous: it tended to be a bit lower in the pool, but the patterns were different (because the stride is so different) and they overlapped a bit.

So what can we take away from this? Not a huge amount — as the researchers point out in their paper, there are a lot of methodological limitations to measuring EMG signals from someone in a dry suit. Also, the stride pattern in pool running is hard to control (the subjects in this case were asked to use the “high-knee” style of pool running rather than the “cross-country skiing” style). If anything, we can say that the lower legs get significantly less stimulation from pool running, so when you do return to dry land, you might want to take extra care looking for aches and pains in your calves and shins. In the end, no one is doing pool running because they think it’s the same as running — and for now, it’s probably the next best thing (unless you have an Alter-G treadmill).

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